1. Field of the Invention
The present invention relates to an ultrasonic probe and an ultrasonic diagnostic apparatus, and more particularly, to an ultrasonic probe and an ultrasonic diagnostic apparatus having a cooling system.
2. Description of the Related Art
An ultrasonic diagnostic apparatus for examining an object by transmitting ultrasonic waves to the object so as to use the reflected waves has been widely used in a medical field. An ultrasonic probe for transmitting/receiving ultrasonic waves is used by bringing its leading end in contact with the object, and the ultrasonic probe includes a plurality of transducers which generate ultrasonic waves while converting received ultrasonic waves into electric signals.
During operation of the ultrasonic diagnostic apparatus, not all the ultrasonic waves generated in the ultrasonic probe transmitting ultrasonic waves are transmitted to the object and part of them is absorbed in the transducers and converted into heat. When a circuit of a transmission/reception part for generating drive signals of ultrasonic waves and processing the received ultrasonic signals from the transducers in an ultrasonic diagnostic apparatus core connected to the ultrasonic probe is housed in the ultrasonic probe, electric power is consumed also in the circuit so as to generate heat.
The ultrasonic probe, as mentioned above, is used by bringing it in contact with a body surface of the object, it is necessary to design the ultrasonic probe so that the surface temperature does not exceed a predetermined temperature for its safety sake.
On the other hand, there is a method for improving the quality of ultrasonic images by increasing the power of transmitting ultrasonic waves so as to increase the S/N (signal to noise) ratio of the received ultrasonic waves. Although the power of transmitting ultrasonic waves has an upper limit for its safety, with increasing S/N ratio within a safe range, the larger S/N ratio can be obtained so as to improve the image quality.
However, if the power of transmitting ultrasonic waves is increased, the heat value in the ultrasonic probe is also increased so as to largely increase the surface temperature of the probe, thereby giving the object discomfort.
Recently, an ultrasonic probe capable of three-dimensional scanning has been developed, which includes two-dimensionally arranged transducers so as to three-dimensionally apply ultrasonic waves, and it has begun limited practical operations. In such an ultrasonic probe capable of three-dimensional scanning, the number of transducers increases in comparison with that of an ultrasonic probe capable of two-dimensional scanning in that transducers are unitarily arranged, so that when the circuit of the transmission/reception part in the ultrasonic diagnostic apparatus core is built in the probe, the scale of the circuit also becomes large.
Accordingly, in the ultrasonic probe capable of three-dimensional scanning, with increasing number of transducers and with increasing circuit scale, the heat value is increased, so that it is difficult to maintain the surface temperature at its front end lower than a predetermined level.
Then, an ultrasonic probe having a cooling mechanism using a refrigerant such as water has been proposed (see, for example, U.S. Pat. No. 5,560,362 or Japanese Patent Application (Laid-Open) No. 2003-38485). The proposed ultrasonic probe has a structure in that a refrigerant is circulated between an ultrasonic diagnostic apparatus core and the front end of the ultrasonic probe via a refrigerant tube attached to a cable of the ultrasonic probe so as to cool the ultrasonic probe. A cooling system, including a pump for passing the refrigerant to the ultrasonic probe and a radiator for cooling the refrigerant, is housed in a probe connector part connecting between the ultrasonic probe and the ultrasonic diagnostic apparatus core or in the ultrasonic diagnostic apparatus core.
FIG. 29 is a diagram showing an example of a structure of a conventional ultrasonic probe having a cooling mechanism. This ultrasonic probe 100 includes a probe unit 110, a compound cable unit 120 and a connector part 130. The probe unit 110 has a transducer part 111 and a heat-receiving part 112. The transducer part 111 transmits and receives ultrasonic waves to and from an object. The heat-receiving part 112 absorbs heat of the transducer part 111. The compound cable unit 120 communicates ultrasonic driving signals to the transducer part 111 and ultrasonic reception signals from the transducer part 111. The connector part 130 connects the compound cable unit 120 and an ultrasonic diagnostic apparatus core 200.
FIG. 30 is a diagram showing a section of the conventional compound cable unit 120 shown in FIG. 29. The compound cable unit 120 includes a multi-core cable 121, a refrigerant supply tube 122, a refrigerant ejection tube 123 and a coating 125. The multi-core cable 121 has signal lines 124 which communicate signals between the probe unit 110 and the connector part 130. The refrigerant supply tube 122 serves as a channel supplying a refrigerant cooled in the ultrasonic diagnostic apparatus core 200 to the heat-receiving part 112 of the probe unit 110 through the connector part 130. The refrigerant ejection tube 123 serves as a channel sending the refrigerant ejected from the heat-receiving part 112 to the ultrasonic diagnostic apparatus core 200 through the connector part 130. The coating 125 sticks and bundles the multi-core cable 121 in which each core has a circular section, the refrigerant supply tube 122 and the refrigerant ejection tube 123.
The compound cable unit 120 of the ultrasonic probe 100 having the cooling mechanism includes the refrigerant supply tube 122 and the refrigerant ejection tube 123 closely arranged outside the multi-core cable 121. Hence, due to the heat from the refrigerant ejection tube 123 for sending the refrigerant ejecting the heat of the heat-receiving part 112, the temperature of the refrigerant in the refrigerant supply tube 122 rises so as to reduce the cooling power of the heat-receiving part 112.
In the geometrical moment of inertia of the compound cable unit 120, as shown in FIG. 30, the geometrical moment of inertia about an axis XX of the length h in the moment direction (the diameter of the multi-core cable 121+a diameter close to that of the refrigerant supply tube 122 or the refrigerant ejection tube 123) is larger than those about axes YY, Y1Y1, and Y2Y2 of a length W in the moment direction close to the diameter of the multi-core cable 121, so that directional difference in bending easiness of the compound cable unit 120 is produced, deteriorating operationality of the ultrasonic probe.
On the other hand, in the ultrasonic probe housing a number of transducers or a number of transducers and a circuit board, the temperature of not only the front end of a probe unit but also of the entire probe unit is increased, so that a safety problem in handling the probe unit arises for an operator of the ultrasonic probe who gets hold it directly with a hand. Since the probe unit is provided with a endothirm part for absorbing the heat, the ultrasonic probe is increased in size, deteriorating the operationality.
When the cooling system is also assembled within the ultrasonic diagnostic apparatus core, it is necessary to circulate a refrigerant via a probe connector part, so that the cost of a connection mechanism for the refrigerant in between the ultrasonic diagnostic apparatus core and the probe connector part is increased while reliability in cooling power is difficult to be secured.
Furthermore, when a cooling system using a refrigerant is assembled within the ultrasonic probe including the probe connector part, since the space within the ultrasonic probe is small, it is difficult to achieve a cooling system with sufficient cooling power while securing reliability in cooling power.
In order to improve the cooling power, it is necessary to increase a radiator for radiating the heat of a refrigerant so as to cool the refrigerant. When a pump for circulating the refrigerant, the radiator, and a container for storing the refrigerant are housed within the probe connector part, the probe connector part is increased in size by the size of the large radiator. The pump for circulating the refrigerant, the radiator for radiating the heat of the refrigerant, and a radiator fan need to be built in the probe connector part, thereby also increasing the probe connector part in size. When increasing the cooling power in such a manner, the cooling system becomes large in size, so that it has been difficult to simultaneously satisfy the improvement of the cooling power and the miniaturizing the cooling system.
When cooling the ultrasonic probe by a cooling system incorporating the conventional technique, even when the temperature of the probe unit is not increased yet, the ultrasonic probe is cooled more than it needs, reducing energy efficiency.